In the electronics mounting field, due to a fear of the nocuous of lead or a rise in concern about the environment, bonding utilizing no lead is desired, and alternative materials have been developed and practicalized as to an Sn—Pb eutectic solder that is a general solder material.
On the other hand, materials alternative to high-temperature lead solder have been considered as the bonding materials for the semiconductor component internal part.
As candidate materials alternative to high-temperature lead solder, exemplified for solder materials are those of Au system, of Bi system, of Zn system, and of Sn system. Regarding the solder materials of Au system, for example, Au-20Sn and the like with the melting point of 280° C. have been partially practicalized but, since their principal ingredients are gold, they are not versatile for such reasons that they are hard in material property, the material costs are high and use is limited to small-sized components.
Bi the melting point of which is in the vicinity of 270° C. is acceptable in respect of the melting temperature but is poor in ductility and thermal conductivity and, for the solder of Zn system, since the elastic modulus is too high, there are problems of a mechanical characteristic and a heat resistance property in internal bonding of a semiconductor component.
On the other hand, regarding the solder materials of Sn system, they are, although having superior mechanical characteristics, poor in heat resistance properties with low melting points being less than 250° C. Hereupon, for the purposes of the heat-resistance-property improvement of Sn system, bonding materials have been considered such that the melting points are raised due to intermetallic compounding by forming CuSn compounds, for example. (see Japanese published patent application 2007-273982).
FIG. 6 is a sectional view of a conventional bonding structure body recorded in Japanese published patent application 2007-273982. In FIG. 6, the power semiconductor module 501 has the bonding part 504 between the power semiconductor element 502 and the electrode 503. For this bonding part 504, a CuSn compound is utilized as a bonding material.